Re: [boost] [variant] Warning: variadic templates in boost::variant

Subject: Re: [boost] [variant] Warning: variadic templates in boost::variant
From: Matt Calabrese (rivorus_at_[hidden])
Date: 2013-12-10 17:09:55

On Tue, Dec 10, 2013 at 1:35 PM, Larry Evans <cppljevans_at_[hidden]>wrote:

> I'm trying to understand how you arrive at the static_visitor.  Since
> the set of bounded types in the variant is a result of
> metaprogramming, I'm guessing that the static_visitor would also have
> to be the result of some metaprogramming.  Otherwise I can't figure
> out how it could be done.

The visitor is not metaprogrammed. The "display" visitor is used for
generic visualization of the variant, regardless of what's inside. It
simply has an operator() template that uses a display function found by ADL
(much like operator<< would be if we were doing generic output to a
stream). If the variant is just variant<>, it makes sense to not display
anything in this particular case. This would all be trivial to do if
variant<> just worked and we specified what happens when you use
apply_visitor on it.

>  I'm guessing that you use some sort of
> inheritance for each bounded type.  Is that right?

No.

-- 
-Matt Calabrese